Climate History & the Cryosphere

Part C: Ocean Impacts

Water is unique among Earth's natural materials. In addition to the essential role it plays in supporting life, water covers a large portion of our planet and has a freezing/melting point that is fairly close to Earth's average temperature. This results in water being present in both liquid and solid forms on Earth's surface, depending on location. Relatively small changes in Earth's average temperature dramatically increase or decrease the amount of Earth's snow and ice. Earth's average temperature today is just a few degrees warmer than it was during the last glaciation, when a large area of the northern United States was buried under 3 to 4 kilometers of ice.

Use the interactive below to explore how glacial ice and sea level have changed over the last 450,000 years of Earth's history.

Read the introductory text. Then click the yellow arrow to continue. You can reset the interactive at any time by clicking the "Start Over" button in the top right corner.

Move the time slider below the graph to trace out Earth's climate history. The thermometer shows average global air temperature. The globe shows glacial ice extent in the northern hemisphere and the cross section shows the ice extent and changing coastlines around the United States.

Use the radio buttons and yellow arrows in the bottom panel of the interactive to learn more about factors that influence global sea level. Then answer the Checking In and Stop and Think questions below.

False You got it! Sea level also can also rise due to thermal expansion. When seawater is heated, it's molecules move faster and farther apart, causing it to expand in volume. Glacier melt and thermal expansion contribute approximately equally to the sea level rise we see today.

Stop and Think

1: Describe how the U.S. coastline during the last glacial age 20,000 years ago compares to the coastline during the interglacial period 125,000 years ago. What factors contributed to these changes?

2: Does the amount of ice on Earth only affect places we typically think of as being "cold"? Explain your reasoning.